This invention relates to an injectable composition consisting of physiologically-compatible bodies, particularly those made of deformable silicone rubber. The composition of the invention is adapted to be used in a method for treating a tissue condition, particularly for tissue augmentation, by injecting said composition into the site of said condition, as described and claimed in application Ser. No. 364,722 (U.S. Pat. No. 5,007,940).
The use of various injectable or inflatable polymeric bodies for tissue augmentation and prosthetic implants is known in the art. For example, U.S. Pat. No. 4,686,962 discloses an assembly for hypodermically implanting a genitourinary prosthesis for the treatment of urinary incontinence which includes an inflatable containment membrane which is inflated by material injected with a hypodermic needle.
Urinary incontinence also has been treated by the transurethral injection of polytetrafluoroethylene (PTFE), usually in the form of a paste or encapsulated particles. See, for example, "Transurethral Polytetra-fluoroethylene Injection for Post-prostatectomy Urinary Incontinence" by M. Kaufman et al, the Journal of Urology, Vol. 132, Sep. 1984, p. 463-464, and the references cited therein. However, if the particles are small, complications arise from undesirable migration or removal by phagocytes causing potential problematical accumulation at other sites, for example the brain, kidney or lungs.
U.S. Pat. No. 4,803,075 discloses an injectable implant composition for soft tissue augmentation comprising an aqueous suspension of a particulate biomaterial, preferably fibrillar cross-linked collagen, and an amount of a biocompatible fluid lubricant.
Another application for tissue augmentation is in the treatment of a hypoplastic breast wherein a typical prior art prosthesis is provided by a silicone membrane enveloping a suitable bulking material, for example a saline solution or a flexible polysiloxane gel. One disadvantage of the saline-containing prosthesis is that microleaks in the silicone membrane or valving mechanism lead to deflation of the prosthesis. A problem with polysiloxane gel is that it contains low-molecular weight compounds, such as cyclic oligomers, which slowly migrate into the patient's system and cause problems similar to those associated with the PTFE particles discussed above.
A solution to the problems associated with earlier polymeric implants is provided by U.S. Pat. No. 4,631,188, which discloses a method of in situ formation of a solid polymer in a mammal which comprises injecting into said mammal a physiologically-acceptable polymeric composition comprising a solution in a water-soluble, non-toxic polar solvent of a water-insoluble, non-toxic, non-cross-linked polymer or copolymer selected from polymers and copolymers of acrylonitrile or vinylacetate, linear or slightly branched polymers and copolymers of 2-hydroxyethylacetate and methacrylate, poly-(N-vinyliminocarbonyl), polycondensates and polyadducts and having a solubility parameter of from about 9.2 to about 15.5 (cal/cc).sup.1/2.
The water-insoluble non-toxic polymers used in the method disclosed in U.S. Pat. No. 4,631,188 fall within the class of compounds known in the art as water-swellable hydrogels and the disclosure in said patent relating to this class of compounds is incorporated herein by reference. As noted in the patent, water-swellable hydrogels have been used in the art for tissue augmentation, usually in implants of defined shape and size. The method disclosed in the patent overcomes problems associated with such preformed implants by injecting a solution of said hydrogel into a mammal resulting in the in situ formation of a solid polymer in the mammal. This method involves the use of a water-soluble polar solvent, for example dimethyl sulfoxide (DMSO), which, although non-toxic, is an unnecessary adjunct to the implant and has to be dispersed by the mammal's metabolism. Furthermore, since the polymer is water-insoluble but water-swellable, formation of the solid polymer is dependent upon the amount of water present in the mammalian tissue and the size and shape of the implant is difficult to control.
U.S. Pat. No. 5,007,940 discloses and claims an injectable composition consisting of a plurality of discrete physiologically-compatible, non-biodegradable, polymeric bodies, said bodies having (i) an average outside diameter of from about 0.005 to 0.20 inch, (ii) reversible deformability of about 20 to 75% of their unstressed outside diameter, and (iii) a lubricious surface.
The preferred injectable composition of U.S. Pat. No. 5,007,940 is based upon a water-insoluble, non-toxic hydrogel which does not contain undesirable solvents. Moreover, the discrete, deformable bodies, since they already contain their full complement of water, retain their individual identity and are stable after injection so that the size and shape of the implant does not alter.
It has now been found that an alternative material which may be used for the discrete, deformable polymeric bodies is medical grade silicone rubber.
However, although this silicone material possesses the desired characteristics for the stated injectable composition it does not have the optimum lubricious surface. Accordingly, to make it suitable for use in an injectable composition the particles thereof are coated with a thin film of a liquid lubricant. As used herein the term thin film means just sufficient lubricant to coat the surface of the silicone rubber bodies without forming a separate liquid phase. It is to be understood that the resultant composition is not a dispersion, suspension or paste but a composition of discrete, deformable bodies having the same physical characteristics as the composition disclosed in U.S. Pat. No. 5,007,940.